POU transcription factors have been shown to be important in the regulation of cell fate decisions during development. We have focused on understanding the function of one POU gene, XlPOU 2, in early neural development. This gene is first expressed in Spemann's organizer at the beginning of gastrulation, making it one of the earliest neural-specific transcription factors detected. Its temporal and spatial pattern of expression suggests that it may be regulatory in the neural inductive process. To test this possibility, we have misexpressed XlPOU 2 by injecting synthetic XlPOU 2 mRNA into specific blastomeres of the 32-cell stage embryo. As a result of this perturbation we have observed a switch in cell fate of the epidermal lineage towards a neuronal phenotype both in intact embryos, and in vitro, in uncommitted ectoderm. These experiments suggest that XlPOU 2 has a role as a proneural gene in neurogenesis, and is involved in the initial decision ectodermal cells must make in becoming either epidermal or neuronal. We have also identified several novel POU genes in zebrafish, and have begun characterizing a Brain-1 related gene, Brn-1r. This gene is 72% homologous with mouse Brn-1 at the amino acid level. Unlike Brn-1, whose expression is restricted to the developing nervous system, Brn-1r is a maternal transcript. During gastrulation, Br-1r is expressed in the dorsal portion of the embryo, in involuting mesoderm. At later stages, Br-1r expression is prominent in the nervous system. Functional studies are underway to determine whether this gene is involved in early patterning in the embryo.
